Life Cycle Assessment of Crop Rotation Systems on Rice Cultivars in Northern Iran

Abstract

The release of environmental pollutants, which partly emanates from the application of chemical inputs, is a major global concern. Attempt to determine the methods to reduce environmental risk of rice cultivation are required. Selecting the best cover crop in rice rotation is necessary. The novelty of this research versus current knowledge is that life cycle assessment (LCA) has not been applied to assess the environmental impacts of crop rotation systems in paddy fields in Iran. Hence, the life cycle of rice cultivars in different crop rotations was assessed in Neka region, northern Iran from 2017 to 2018. All the management practices/inputs of local (‘Tarom Hashemi’) and improved (‘Shiroodi’) rice cultivars were monitored. After recording the data of 100 selected paddy fields for each cultivar, nine cover crop-rice rotations (fallow-rice, clover-rice, rape seed-rice, wheat-rice, barley-rice, faba bean-rice, garlic-rice, lettuce-rice and cabbage-rice) were identified. Functional unit of LCA was 1-ton rice yield. The results demonstrated that the maximum and minimum amount of nitrogen, phosphorus and potassium were applied in fallow-rice and clover-rice rotations, respectively. The highest paddy yield for local (4856 kg ha−1) and improved (7745 kg ha−1) cultivars was produced in clover-rice rotation. Fossil CO2 eq, biogenic CO2 eq, global warming potential (GWP) 100a, terrestrial acidification (TA) and fossil depletion (FD) of local cultivar were 11.79%, 34.76%, 13.35%, 15.48%, and 20.13% greater than improved cultivar. The most cumulative energy demand (CED) in both cultivars was obtained for fallow-rice rotation followed by rape seed-rice rotation. The highest emission of biogenic CO2 eq for both cultivar was observed in rape seed-rice and fallow-rice rotations. The lowest amount of GWP 100a was calculated in clover-rice rotation for local and improved cultivars (248.08 and 240.5 kg CO2 eq). In both cultivars, the most and lowest amount of TA, freshwater eutrophication (FEU), ozone depletion (OD) and FD was emitted in fallow-rice and clover-rice rotations. Among the crop rotations, clover-rice and fallow-rice had significantly lowest and most emission of heavy metals in the air, water and soil, respectively. As a matter of fact, the environmental emissions of the study is straightly linked to the application of inputs and field management practices. According to this, the lowest amount of environmental emissions for both cultivars was observed in clover-rice rotation. The emissions released from environmental pollutants are positively correlated with the application of inputs and field management practices for crop species in rotation system. In conclusion, clover-rice rotation showed the potential to save non-renewable energies (fuel, nitrogen, and etc.) with higher paddy yield which is considered to be environmentally friendly crop in rotation with respect to reduce emissions of GHG.